Microminiature mechanical switches offer an alternative to semiconductor electronic components as a means for signal switching. U.S. Pat. No. 5,047,740 to Alman describes a miniature switch for controlling microwave signal transmission. A spring-loaded mechanism is controlled by a magnetic solenoid to connect a first microwave signal line to either a second or a third microwave signal line. Solenoid activation pivots an armature which determines the positioning of jumpers relative to the microwave signal lines.
An electrostatically actuated micromachined rotary switch is described in U.S. Pat. No. 5,121,089 to Larson. The rotary switch is fabricated on an integrated circuit wafer using integrated circuit fabrication processing. Microwave transmission lines are positioned to contact a rotating blade of the switch when the rotating blade is properly aligned. Rotation of the blade is controlled by electrostatic fields created by control pads and other switch elements formed on a substrate that also contains the microwave transmission lines.
In a paper entitled "Thermo-Magnetic Flexure Actuators," 0-7803-0456-X/92, 1992 IEEE, Guckel et al. of the University of Wisconsin describe an actuator that utilizes one or both of thermal effects and magnetic forces to cause deflection of beams when an electrical current is applied. While this structure functions well in certain applications, there are difficulties. For example, if the Guckel et al. actuator were to be used as a switch to conduct a signal from the beams to structure that contacts the beams following deflection, signal transmission would be susceptible to feedthrough from the actuator-deflection current. Another difficulty involves inconsistent and even conflicting design requirements for different components of a transmission scheme. A signal line design requires the selection of materials and dimensions to yield a suitable impedance and to minimize signal loss. On the other hand, the actuator of Guckel et al. is designed to achieve a desired deflection in a reliable and efficient manner.
The previously identified patent to Alman lists a number of concerns in the design of a micromachined switch. The switch must be non-particulating and must be adjustable to compensate for changes in the forces which initiate the switching action, e.g., magnetic forces. Moreover, the switch must be reliable over many switching cycles.
What is needed is a microminiature signal switch which minimizes the compromises between fabricating a switch and fabricating signal lines, and which reduces space and cost requirements over conventional combinations of micromachined switches and signal lines.